refactor (v2): better arch

Co-authored-by: Copilot <copilot@github.com>

crates/application/src/config.rs

@@ -0,0 +1,33 @@
+/// Application-level configuration. Auth and infra adapter config lives in their own crates.
+#[derive(Debug, Clone)]
+pub struct AppConfig {
+    pub base_url: String,
+    pub smart: SmartConfig,
+    /// When false the `/auth/register` endpoint returns 403.
+    pub allow_registration: bool,
+}
+
+#[derive(Debug, Clone)]
+pub struct SmartConfig {
+    pub neighbour_limit: usize,
+    pub min_similarity: f32,
+}
+
+impl Default for SmartConfig {
+    fn default() -> Self {
+        Self {
+            neighbour_limit: 10,
+            min_similarity: 0.7,
+        }
+    }
+}
+
+impl AppConfig {
+    pub fn from_env() -> Self {
+        Self {
+            base_url: std::env::var("BASE_URL").unwrap_or_else(|_| "http://localhost:3000".into()),
+            smart: SmartConfig::default(),
+            allow_registration: true,
+        }
+    }
+}